This invention relates to CATV and pay TV, and more particularly to two-way CATV systems.
There have been many variations of pay television and subscription television systems, such as over-the-air, coin operated, multiple wiring, and other configurations, most of which have not been commercially employed to any great extent although the subject of much patent literature. The field of community antenna television systems, or CATV, has more recently tended toward usage of modern electronic communication and data processing techniques and a substantial body of art has developed in what are known as two-way or bidirectional CATV systems. In the category of systems with which the present disclosure is concerned, a central station is employed which includes some type of processing and interrogating system, now typically a general purpose or special purpose computer having both substantial storage and processor capability. The central station also includes television transmission facilities for transmitting a substantial number of programs, some of which are "free" programs for the subscribers, and the extent of use of which need not be monitored, while other programs are special or premium programs such as first run motion pictures, the selection of which by a subscriber requires an appropriate payment. There are also other possible categories of programs, including particularly the specialized or limited access type of program, here termed restricted premium programs, to which only certain subscribers are to be permitted access. These may include, for example, specialized presentations for professional medical, legal, business, social or governmental groups.
There are a number of approaches to controlling access to programs in a two-way CATV, some of which involve recording systems, coin operated systems, special pre-paid descramblers and the like. These approaches however are characterized by the common difficulties of cumbersome and unreliable accounting, supply or collection procedures, and it is generally preferable to utilize the central control and accounting functions of a two-way CATV system for such purposes. A number of two-way CATV systems are known which incorporate features intended to provide a degree of central control and monitoring of program content and usage. Some of such systems employ frequency division multiplexing for data interchange, with a number of different frequencies being utilized in combination to effect command and control. More advanced systems utilize a combination of serial digital data in both upstream and downstream directions that is frequency multiplexed with the video and audio channels, and interrogate the terminals using a time division multiplex mode. Some of such systems employ a combination of frequency shift keying in one band in the downstream direction, with phase shift keying in another band in the upstream direction, to simplify the receiving and transmitting circuitry at the numerous subscriber terminals. Circuits may also be employed at the terminals for assembling messages to be returned to the central station.
The most relevant art pertaining to advanced two-way CATV systems using FSK or PSK upstream and downstream transmissions discusses, but does not show, high speed interrogation or polling techniques. A number of treatments can be found in the literature as to the general organization of systems for high speed interrogation of the subscriber terminals, sometimes only in intermittent fashion as at the start of a program, and other times in overlapping precisely sequenced fashion in which successively more remote subscribers are interrogated in turn. There are descriptions in the literature of systems intended to serve hundreds of thousands and even up to a million subscribers. Such generalized treatments do not confront the substantial technical problems that are encountered in practice in communicating between a central station and a substantial number, say 10,000 to 20,000 or more, of subscribers. In a multiple branch network of this kind the signals are in fact delayed, distorted and attenuated from many causes and to varying extents, so that intercommunication is far from ideal. Cumulative delays from various sources greatly reduce the interrogation rate, if reliable intercommunication is to be achieved, but there is a particular need for correct data in a CATV system because of the inevitable customer reaction to incorrect billings.
There is a separate line of development in communications and CATV technology, in which special noise measuring or distortion measuring circuits are included in the system, along with controllable mechanisms for selectively adjusting the gain, bandpass, slope and other amplifier characteristics, or for selectively blocking off sources of noise in the system in order to enable one remote transmitter out of a substantial number of transmitters to be received at the central station with a signal having an adequate signal-to-noise ratio. Extensive controls of this kind, however, not only impose a substantial economic burden on the system, but also demand processor and equipment time and involve their own operating problems.
An interactive two-way CATV system should be able to provide useful interchanges between the central station and the individual terminals. Some systems have gone as far as to propose transmission of both video and audio in both directions between the subscribers and the central station, or between individual subscribers. The incorporation of such features, however, would not permit general usage in CATV systems, because of the attendant cost. Systems are known which provide a number of individual desirable features, such as program previewing without cost, accurate accumulation of usage data, protection against unwanted usage of pay programs, ability to interrogate subscribers, and capability for indicating the existence of fire, emergency or other alarm conditions. However, such features have generally been provided on an isolated basis in individual systems, and the prior art has not heretofore disclosed an arrangement that is at the same time highly versatile, economical and of practical utility.
The following patents are illustration of the art:
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